Conventionally, a lighting condition (that is, luminance distribution in a scene) which is produced depending on the layout and so on of lighting equipments has been simulated. An image with luminance distribution predicted from this lighting simulation is utilized for designing the luminance condition as a reference image.
However, how a person perceives brightness (referred to as “brightness impression” herein) does not directly correspond to values of luminance. For example, when in a luminance image, a peripheral area with lower luminance than an object area is compared with a peripheral area with higher luminance than an object area, the person perceives the former object area as brighter than the latter, even when both the object areas are equal in luminance. Note that the brightness impression is sometimes called brightness perception.
Therefore, predicting accurate luminance distribution by the above lighting simulation and referring to an image with the obtained luminance distribution are not sufficient to study a luminance condition at the time of designing it. This is because brightness impression of an object area changes depending on luminance of a peripheral area even with no change in the luminance of the object area.
In order to study the luminance condition sufficiently, in recent years there has been a demand for quantitative prediction of brightness impression of an object area of a luminance image. The present inventors have proposed a technique to quantitatively predict brightness impression of an object area with high accuracy even in a case where luminance distribution is complicated as in an actual scene (see, for example, a patent document 1). Further, applying this technique extensively makes it possible to transform a luminance image to a brightness image.
Patent document 1 Japanese Unexamined Patent Application Publication No. 2004-61150